Electrostatic precipitator for the collection of particles contained in a gas

ABSTRACT

Particles suspended in polluted gas or atmospheric air to be analyzed and purified are charged and precipitated in a single unit comprising a leak-tight chamber of substantial length, an admission duct for the gas to be analyzed and a &#39;&#39;&#39;&#39;clean&#39;&#39;&#39;&#39; gas supply duct which are parallel and open into one end of the chamber, at least one outlet duct being located opposite to the admission duct at the other end of the chamber. The chamber contains at least two electrodes, one of which is a conductive plate adjacent to the admission and outlet ducts, the other being at least one electrode such as a conductive wire which produces a corona discharge in the gas.

nited States Patent [191 Volsy Aug. 6, 1974 ELECTROSTATIC PRECIPITATORFOR THE COLLECTION OF PARTICLES CONTAINED IN A GAS [30] ForeignApplication Priority Data Dec. 31, 1971 France 71.47801 [52] U.S. Cl55/121, 55/128, 55/146, 55/151, 55/152, 55/270, 73/28, 324/71 CP [51]Int. Cl. B03c 3/04 [58] Field of Search 55/146, 150, 151, 152, 55/128,129, 120, 121, 270; 324/32, 33, 71

R, 71 CP; 73/23 R, 28; 310/81, 317/3, 4

[56] References Cited UNITED STATES PATENTS 2,097,233 10/1937 Meston55/152 X 2,868,318 1/1959 Perkins et a1. 55/151 3,331,192 7/1967Peterson 55/107 3,413,545 11/1968 Whitby 317/3 X 3,516,608 6/1970 Bowenet al. 239/3 X 3,520,172 7/1970 Liu et al. 55/138 X 3,526,828 9/1970Whitby 324/71 CP X 3,561,253 2/1971 Dorman 310/8.1 X 3,656,440 4/1972Grey 110/8 R 3,718,029 2/1973 Gourdine et a1 73/28 FOREIGN PATENTS ORAPPLICATIONS 833,798 3/1952 Germany 55/D1G. 38

Primary Examiner-Dennis E. Talbert, Jr. Attorney, Agent, or FirmCameron,Kerkam, Sutton, Stowell & Stowell [57] ABSTRACT Particles suspended inpolluted gas or atmospheric air to be analyzed and purified are chargedand precipitated in a single unit comprising a leak-tight chamber ofsubstantial length, an admission duct for the gas to be analyzed and aclean gas supply duct which are parallel and open into one end of thechamber, at least one outlet duct being located opposite to theadmission duct at the other end of the chamber. The chamber contains atleast two electrodes, one of which is a conductive plate adjacent to theadmission and outlet ducts, the other being at least one electrode suchas a conductive wire which produces a corona discharge in the gas.

8 Claims, 1 Drawing Figure ELECTROSTATIC PRECIPITATOR FOR THE COLLECTIONOF PARTICLES CONTAINED IN A GAS This invention relates to anelectrostatic precipitator for the collection of particles in a gas suchas air.

More precisely, the present invention is concerned with a device for thecollection of polluting particles contained in a sample of atmosphericair. The device also permits the removal of dust from a gas andconsequently the purification of this latter. By collecting theimpurities contained in the atmosphere or in any other gas, it ispossible to carry out both a qualitative and quantitative analysis ofsaid impurities or in other words to determine the concentration ofimpurities and to perform a chemical analysis of said impurities.

Control of air pollution, especially in large urban areas, constitutes aproblem of considerable importance. Many types of particle collectionequipment are already in use and among these can be mentioned:

systems of filtration through porous fabrics; by means of these systems,the pores choke at a very high rate and the device rapidly becomesinoperative;

inertial systems based on gravity settling, particle impact orcentrifugal force; the disadvantage of these systems lies in their lowcollection efficiency in the case of particles which have a small mass(for example particles smaller than 1 micron in'diameter);

the thermal precipitation systems (bombardment of photons); on thecontrary, these systems permit retention only of particles which have avery small mass;

electrostatic precipitation devices; as a rule, these devices consist ofa pin or a wire which serves as an ion source and is placed along theaxis of a cylinder of revolution, the particles being precipitated onthe cylinder walls. Recovery of the deposits thus obtained is adifficult operation and the efficiency of this type of apparatusdecreases very rapidly in time as the particle deposits are formed onthe wire; moreover, the design concept of these devices precludes anyautomatic adaptation to the measurement of particle concentration.

The precise object of the present invention is to provide anelectrostatic precipitator for the collection of particles contained ina gas which overcomes the disadvantages attached to the techniques ofthe prior art which were mentioned in the foregoing.

The electrostatic precipitator for the collection of particles containedin a gas essentially comprises:

a leak-tight chamber of substantial length, a first inlet duct for theadmission of gas to be analyzed and a second inlet duct for the supplyof clean gas which are located in parallel relation and have theiropenings at one end of said chamber, at least one outlet duct locatedopposite to the first inlet duct at the other end of said chamber, atleast two electrodes having different functions being placed within theinterior of said chamber, one electrode being a conductive plate locatedclose to that wall of said chamber which is adjacent to the first andthird ducts, the geometry of the other electrode or electrodes beingsuch as to produce in conjunction with the conductive plate a coronadischarge in the gas which is present within said chamber;

deflectors which provide a separation both at the inlet and at theoutlet between the gas streams of the ducts while ensuring relativeindependence between the polluted gas stream which is admitted throughthe first duct and discharged through the third duct, and

the clean gas stream which is admitted through the second duct;

a generator which serves to deliver direct or modulated current andapplies a direct-current potential difference between the electrodes.The electrode which produces the corona discharge can be, for example,either a conductive wire which is parallel to said plate or a conductivepin which is located at right angles to said plate.

The gases are introduced through the first and second ducts. In apreferred embodiment, provision is made for a suction device within thethird duct. In another preferred embodiment, the electrode whichproduces the corona discharge is placed in the line of extension of thesecond duct.

By means of the device in accordance with the invention, the same systemformed by the electrodes therefore serves to carry out both the chargingof the particles contained in the polluted gas to be analyzed and tocause precipitation of said particles.

Charging of the particles is produced by the ionized molecules of airresulting from corona discharge by applying a potential differencebetween the electrodes.

The particles which are thus ionized are received by the plate under theaction of the electrostatic field applied between the plate and theelectrode which produces the corona discharge. Vortices arising from theelectric wind are eliminated while ensuring a flow of clean gas betweenthe electrodes, which prevents any loss of aerosols on the walls of thecollection chamber. This result is obtained under very good conditionsby placing the corona discharge electrode in the axis of the clean gassupply duct or in an extreme position corresponding to the inlet of thetwo ducts for the admission of clean gas and polluted gas.

A clearer understanding of the invention will in any case be gained fromthe following description of one embodiment of the invention which isgiven by way of non-limitative example. Reference is made in thedescription to the single accompanying FIGURE in which the deviceaccording to the invention is shown in longitudinal cross-section.

The electrostatic device for collecting particles in a gas as shown inFIG. 1 essentially comprises a leak-tight chamber 2 of substantiallength and having a parallelepipedal shape, for example, said chamberbeing connected at one end to the inlet ducts 4 and 6 and at the otherend to the outlet duct 8. The chamber 2 is provided internally with aconductive metallic plate 10 which is fixed on the bottom wall of saidchamber 2 and electrically insulated from said wall. Provision is alsomade within the chamber 2 for a conductive wire 12 which is parallel tothe axis of this latter and placed in the line of extension of the inletduct 6. Said wire is maintained in position by means of two insulatingsupports 14 and 14'. An electric current generator 16 serves to applybetween the conductive wire 12 and the plate 10 a direct-currentpotential difference V In this example, the duct 8 is connected to asuction device 17 of known type. Within the chamber 2, the gas streamscorresponding to the inlet ,ducts 4 and 6 are partially separated by thedeflectors l8 and 18'. In this example, the chamber 2 is provided withan outlet duct 20 which is located in the line of extension of the inletduct 6.

In one alternative form of construction, the duct 20 is fitted with anadjustable closure system 22.

in the precipitator shown in the FIGURE, the electric conductor whichproduces the corona discharge in conjunction with the conductive plateis a conductive wire 12 located parallel to the axis of the chamber 2but, as has been stated earlier, the electric conductor can consist of aconductive pin placed at right angles to the conductive plate 10.

The operation of the device is immediately apparent from the foregoingdescription. The polluted gas which is introduced into the chamber 2through the inlet duct 4 is ionized by virtue of the assembly consistingof the conductive wire 12 and the plate 10. The wire 12 behaves as acharge emitter since it is subjected to the corona effect and applies apotential difference V between the wire 12 and the plate 10. The gas isaccordingly ionized and the ion space charge confers a charge on theparticles in suspension in the gas. These charged particles are thenattracted by the plate 10 which has the same effect as a collectingplate and thus collects the particles contained in the polluted gas. Thegas which is introduced through the duct 6 and can be either a clean gasor the gas which is withdrawn from the duct 8 compensates for theelectric wind produced by the corona discharge. This prevents anyformation of vortices and any deposition of particles on the walls ofthe chamber 2 other than the plate 10. The rate of flow of the gasinjected into the duct 6 can advantageously represent to 30 percent ofthe throughput of polluted gas.

By way of indication, the rate of flow of the gas within the chamber 2under the action of the suction device 17 can advantageously be withinthe range of 10 to 400 cm/second; the direct-current potentialdifference V applied between the plate 10 and the conductive wire 12 canbe within the range of 2 to 40 kV whereas, in a preferred embodiment,the length of the chamber 2 can range from 3 to 30 cm according to thevoltage applied, the rate of propagation of the gas and the percentagecontent of impurities.

In order to perform automatic measurement of the particle concentrationof the polluted gas, the collecting plate 10 can be adapted to anautomatic measuring device which can be constituted by an electrometer,by a piezo-electric strip or by a moving film and the quantity ofpolluted gas introduced into the apparatus can be measured by means of aflowmeter.

Should it be desired to remove dust from a gas, means can be providedfor cleaning the plate 10 by scraping or sweeping said plate, forexample.

Tests carried out with a device of this type on the basis of pollutedand opaque gas of a smoke-producing charge have shown that the pollutedair delivered at the discharge end was wholly transparent andundetectable by the naked eye. All the particles were precipitatedtional design, is therefore inexpensive to produce and also has veryhigh reliability of operation; by virtue of the fact that the particlesare collected on a single flat plate, removal of said particles forsubsequent chemical analysis presents no difficulty.

It can readily be understood that the present invention is not limitedto the example which has been more especially described with referenceto the accompanying drawing; on the contrary, all variants are includedwithin its scope, especially the alternative form of construction inwhich the bottom wall of the chamber 2 is replaced by the plate 10.

What we claim is:

1. An electrostatic precipitator for the collection of particlescontained in a gas, wherein said precipitator comprises:

a leak-tight chamber of substantial length, a first inlet duct for theadmission of gas to be analyzed and a second inlet duct for the supplyof clean gas which are located in parallel relation and have theiropenings at one end of said chamber, at least one outlet duct or thirdduct located opposite to said first inlet duct at the other end of saidchamber, at least two electrodes having different functions being placedwithin the interior of said chamber, at least one other of saidelectrodes being a conductive plate located close to that wall of saidchamber which is adjacent to the first and third ducts, the geometry ofat least one other of said electrodes being such as to produce inconjunction with the conductive plate a corona discharge in the gaswhich is present within said chamber;

deflectors which provide a separation both at the inlet and at theoutlet between the gas streams of the ducts while ensuring relativeindependence between the polluted gas stream which is admitted throughthe first duct and discharged through the third duct, and the clean gasstream which is admitted through the second duct;

a direct-current generator which applies a directcurrent potentialdifference between the electrodes.

2. A precipitator according to claim 1, wherein the corona-dischargeelectrode is located in the line of extension of the second duct.

3. A precipitator according to claim 1, wherein the electrode whichproduces the corona discharge is a conductive wire in substantiallyparallel relation to the conductive plate.

4. A precipitator according to claim 1, wherein the electrode whichproduces the corona discharge is a conductive pin located at rightangles to the conductive plate.

5. A precipitator according to claim 1 wherein, the third duct includesa suction device.

6. A precipitator according to claim 1, including a fourth duct oppositeto the second duct and said fourth duct having a device for varying theopening of said duct.

7. A precipitator according to claim 1 wherein said conductive plate isconnected to a measuring apparatus.

8. A precipitator according to claim 1 including a cleaning system forsaid conductive plate.

l l l

1. An electrostatic precipitator for the collection of particlescontained in a gas, wherein said precipitator comprises: a leak-tightchamber of substantial length, a first inlet duct for the admission ofgas to be analyzed and a second inlet duct for the supply of''''clean'''' gas which are located in parallel relation and have theiropenings at one end of said chamber, at least one outlet duct or thirdduct located opposite to said first inlet duct at the other end of saidchamber, at least two electrodes having different functions being placedwithin the interior of said chamber, at least one other of saidelectrodes being a conductive plate located close to that wall of saidchamber which is adjacent to the first and third ducts, the geometry ofat least one other of said electrodes being such as to produce inconjunction with the conductive plate a corona discharge in the gaswhich is present within said chamber; deflectors which provide aseparation both at the inlet and at the outlet between the gas streamsof the ducts while ensuring relative independence between the pollutedgas stream which is admitted through the first duct and dischargedthrough the third duct, and the ''''clean'''' gas stream which isadmitted through the second duct; a direct-current generator whichapplies a direct-current potential difference between the electrodes. 2.A precipitator according to claim 1, wherein the corona-dischargeelectrode is located in the line of extension of the second duct.
 3. Aprecipitator according to claim 1, wherein the electrode which producesthe corona discharge is a conductive wire in substantially parallelrelation to the conductive plate.
 4. A precipitator according to claim1, wherein the electrode which produces the corona discharge is aconductive pin located at right angles to the conductive plate.
 5. Aprecipitator according to claim 1 wherein, the third duct includes asuction device.
 6. A precipitator according to claim 1, including afourth duct opposite to the second duct and said fourth duct having adevice for varying the opening of said duct.
 7. A precipitator accordingto claim 1 wherein said conductive plate is connected to a measuringapparatus.
 8. A precipitator according to claim 1 including a cleaningsystem for said conductive plate.